1. Field of the Invention
The present invention relates to a device for modulating the sensitivity of a line-transfer photosensitive device.
Photosensitive devices in which scanning is performed by line transfer are already known and have been described in particular in French patent Applications No. 80 09112 and No. 81 07672 filed in the name of Thomson-CSF.
2. Description of the Prior Art
It will be recalled in general terms that a device of this type has a photosensitive zone consisting of M lines each made up of N photosensitive points. The photosensitive points of the different lines are connected in parallel to a memory by means of conductive columns. The signal charges collected on a line of photosensitive points and transferred to the columns are caused by the memory to undergo a periodic transfer from the columns to a read register. In addition, the parasitic charges which are present in tne columns before the signal charges of one of the lines arrive on the columns are periodically transferred by the memory to an evacuation drain.
Known types of line-transfer photosensitive devices have a light sensitivity which is not variable. However, for the different applications of these devices such as cameras available to the general public or in the field of robotics and the like, it is an advantage to have the possibility of using the equivalent of a diaphragm or, in other words, of modulating the sensitivity of the device as a function of the incident light.
It is known to modulate the sensitivity of photosensitive devices in the solid state by varying their integration time.
Up to the present time, however, the basic design concept of line-transfer devices having a light sensitivity which can be varied by modulating the integration time has given rise to problems and the present invention provides the answer to these problems.